Directional antenna array



Sept. 5, 1967 H w SULLlVAN ET AL 3,340,530

' DIRECTIONAL ANTENNA ARRAY Filed Dec. 30, 1963 s Sheets-Shed 1 WAVEFRONT OF TRANSMITTED WAVE FIG. I

PRIOR ART DIRECTION 0F PROPAGATION l3 d SIN m A SOURCE I |5-A l5-B l5-C15-0 l5-E COS(wt 58) COS(wI 49) COSIWI I4 39) COSIWI'I'ZG) COSIWH'ISICOSIWII 7 e 5 4 s 2 I o I CUMULATIVE TRANSIV"TTEDI mcomme g ls/ E I{WAVE FRONT GROUND TRANSMITTER I I I I. q u I D4 25-7 0 25-3 I INVENTORSHERBERT w SULLIVAN JOHN F. BANZHAF III ATTORNEYS DIRECTIONAL ANTENNAARRAY Filed Dec. 30, 1963 5 Sheets-Sheet 2 FiG. 3

INDIVIDUAL RADIATING ELEMENTS --FISH NET TYPE ANTENNA CORNER TOMODULATOR AND POWER SUPPL TOR INVENTORS HERBERT W. SULLIVAN JOHN EBANZHAF J11 ATTORNEYS Sept. 5, 1967 w SULLWAN ET AL 3,340,530

DIRECTIONAL ANTENNA ARRAY Filed Dec. 30, 1963 5 Sheets-Sheet 5INSTRUMENTATION AND SENSING DEVICES SUCH AS PART! E DE CTORS, RADIA N DECTOR ETC.

INVENTORS HERBERT W. SULLIVAN JOHN F BANZHAFIII Y a /(g w ATTORNEYS S p9 H. w. SULLIVAN ETAL 3,340,530

DIRECTIONAL ANTENNA ARRAY Filed Dec. 30. 1963 5 Sheets-Sheet 4 POWER 7OSUPPLY 72 73 74 TRANS CODE/ DUCER CONVERTER" KEYER ELEMENTS 42 OF THEARRAY 45 DIRECTION OF PROPAGATION 92 INVENTORS HERBERT W. SULLIVAN JOHNF. BANZHAF JIE ATTORNEYS Sept. 5, 1967 H w SULLWAN ET AL 3,340,530

DIRECTIONAL ANTENNA ARRAY Filed Dec. 30, 1963 5 Sheets-Sheet DIRECTIONOF PROPAGATION INVENTORS HERBERT w. SULLIVAN JOHN E BANZHAF IIJIATTORNEYS United States Patent 3,340,530 DIRECTIONAL ANTENNA ARRAYHerbert W. Sullivan and John F. Banzhaf III, New York, N.Y., assignorsto Lear Siegler, Inc., Long Island City, N.Y., a corporation of DelawareFiled Dec. 30, 1963, Ser. No. 334,228 9 Claims. (Cl. 343100)established. As a general matter, the diiferent types of antenna systemscan be grouped into three main categories, in accordance with the typeof communications system being used. The first of these categoriesincludes the socalled passive types of antenna systems. Here, in orderto transmit information from a first station to a second station remotefrom the first, the first station beams energy toward the second. Thesecond station is provided with a directional or non-directional passiveantenna reflector system which receives the energy and reflects it backtoward the first station. If desired, the second station can alsomodulate the received energy in some suitable manner to impressinformation upon it.

In the second category of antenna systems a nondirectional (oromnidirectional) active antenna is used at the station remote from thefirst station. In this case the remote station carries its owntransmitter which transmits radio frequency energy modulated withinformation in a desired manner back to the first station. The thirdcategory of antennas are those of the active directional type, which maybe used by a remote station which carries its own transmitter. Here theantenna at the remote station transmits a directional beam of energyback toward the first station. A

While each of the three types of antenna systems described above hascertain advantages for various applications, these same systems alsohave disadvantages which are inherent in their operation for any givenapplication. In the passive or reflective type of antenna system, forexample, no transmitter is needed at the remote station. Also, there isno problem of orienting the station when an omnidirectional passivereflector is used. However, when this type of passive antenna system isused the first station must transmit a large quantity of power in orderfor an adequate amount of energy to be received at the remote stationand reflected back to the first station. This, of course, greatlyincreases the size and complexity of the transmitter at the firststation. Similarly, while the second type of system, using -atransmitter and omnidirectional antenna at the remote station, also hasno problem of orienting the remote stations antenna, it imposes therequirement of a relatively large transmitter at the remote station whenthe first station is located a considerable distance away. Where thesecond station is unattended and/or inaccessible, any failure of itstransmitter destroys communication between the two stations. While thethird type of system using a transmitter and directional antenna at theremote station does not necessarily need the large transmitter requiredby the omnioriented in such a way so that the remote stationsdirectional antenna points toward the first staion.

directional antenna, it should be understood that the remote stationand/ or its antenna must be stabilized and ice In many cases, forexample in a communications satellite, the problem of orienting thestation and/or its antenna with respect to the first station is so greatthat the advantages obtained by using directional antennas are oftenoutweighed by disadvantages introduced by the orientation equipment. Ittherefore becomes desirable to provide an antenna system which has theadvantages of a directional antenna but does not introduce all of theproblems and equipment associated with orientation. The latter meansthat the antenna should be capable of operating over a fairly largeangular range. One antenna system which has been designed to accomplishthis is the so-called electronically scanned antenna. In this type ofsystem \an antenna array is provided which has a number of elements andthe phase of the energy supplied to the various elements is controlledin a manner to produce a beam of energy in a given direction within thelimits imposed by the antenna construction. While the elec- .tronicallyscanned antenna is a partial solution to the problem of providingdirectivity of the energy beam and reducing the orientation problem tosome extent, this type of system also has disadvantages in that it needssome type of programmer, usually a computer, to control the phase shiftof the energy between the elements and it also needs the phase shifters.Hence, many of the advantages introduced by this type of antenna areoften outweighed by its disadvantages in some applications.

The present invention is directed to an antenna array which combinesvarious advantages of several of the foregoing systems. In accordancewith the invention, a transmitting antenna array is provided which isdirectional, thereby reducing the transmitter power requirements at theremote station, and which is capable of operating over a rather largeangular range, thereby reducing the orientation problem. The antennaarray of the present invention is formed by a plurality of separateradiator elements, each of which has its own antenna and oscillator. Theoscillators of the elements in the array are designed to oscillate atthe same frequency and they are triggered or phase alignedby theincoming energy received by the individual elements antenna from anotherstation. The signals produced by the various oscillators of the arrayare radiated by the antennas of the individual elements. While thesignals are all of the same frequency, they are of different phases .asdetermined by the incoming signal which triggers the oscillators. Thisarrangement produces a transmitted beam of energy whose phase frontprop-agates in the same direction as the phase front of the incomingwave. By reversing the direction of the beam of energy produced by theoscillators, such as by a reflector or other suitable means, the beamcan be transmitted back toward the direction from which the incomingwave originated. Thus, if the original wave is produced by a firststation, a second station carrying the antenna array can communicatewith the first station by any suitable techniques such as by modulatingthe energy produced by the element oscillators.

As can be seenthe antenna array of the present invention produces adirectional beam of energy which is transmitted back to the stationwhich produced the wave which triggered the element oscillators of thearray. Thus, the antenna array has the advantages of a directional typeof antenna. At the same time, the antenna array is capable of operatingover a fairly wide angular range, which in some cases may be extendedover a complete spherical configuration. This substantially eliminatesthe orientation problem. Also, the array of the present invention doesnot need or use the programmer and phase shifters normally associatedwith electronically scanned antennas even though it is capable ofoperating over a large angular range. This greatly reduces thecomplexity of the asso- It is therefore an object of the presentinvention to provide an antenna array having a plurality of oscillatorswhich are triggered by an incoming wave.

A further object of the invention is to provide an antenna array whichresponds to an incoming signal to produce a directional beam of energy.

Still a further object of the invention is to provide an antenna arrayin which a plurality of oscillators are triggered by an incoming wave toproduce signals at the same frequency but of different phases, thesesignals being combined to produce a wave which is transmitted in thesame direction as the incoming wave.

Yet another object of the invention is to provide a directional antennaarray in which a plurality of oscillators respond to an incoming wave toproduce a wave which travels in the same direction as the incoming waveand a reflector is also provided to reflect the wave produced by theoscillators back in the direction from which the incoming wave came.

Other objects and advantages of the present invention will become moreapparent upon reference to the following specification and annexeddrawings in which:

FIGURE 1 is a schematic drawing illustrating the operation of aconventional electronically scanned antenna;

FIGURE 2 is a drawing showing a linear antenna array made in accordancewith the principles of the present invention and illustrating certainoperating features thereof;

FIGURE 3 illustrates the operating principles of the array of FIGURE 2when used with a reflector;

FIGURE 4 is a perspective view of an antenna made in accordance with theprinciples of the invention;

FIGURES 5 and 6 are perspective views showing various arrangements formounting the antenna array of FIG- URE 4;

FIGURE 7 is a schematic diagram of one type of circuits for use as thearray element;

FIGURE 8 is a schematic diagram of one type of modulator system for usewith the antenna of the present invention; and

FIGURES 9 and 10 show other types of antenna arrays using the pluralityof oscillators.

To explain certain of the operating principles of the present inventionreference is made to FIGURE 1 which shows a linear array of radiatingelements 11A to ll-F of a conventional electronically scanned antenna10. The elements 11 are separated from each other by a distance d andare fed from a source 13 of radio frequency energy through a number ofphase shifters ISA-15E. Each phase shifter 15 is interposed between twoadjacent elements and illustratively introduces a phase shift 0 in theenergy to be transmitted. Thus, the energy radiated by element 11D leadsthe energy radiated by element 11E by this angle 0 while the energy ofthe last element 11F in the array lags the energy of element 11A closestsource 13 by an amount 50. The phase of the energy radiated by eachelement is shown adjacent to it.

The phase difference between two elements can be translated into a timedifference between the times that two identical waves of the same phaseleave adjacent elements, D and E for example, in the time for onecomplete cycle of the radiated energy wave the wave will travel adistance of 0/ or (.0 The distance that a wave will travel in timecorresponding to the phase shift 0 is then 1 Zarf The electronicallyscanned antenna array of FIGURE 1 can be considered as having a numberof radiating elements which generate a number of identical signals ofthe same frequency and phase, each signal leaving 0 before the one afterit and traveling a distance before the wave from the next adjacentelement leaves. Therefore, a constant phase front wave will be producedat an angle at with respect to the array which is given by The distancethat the wave travels in reaching the phase front is shown adjacent eachelement. By varying the phase delay introduced by each of the phaseshifters 15 the angle a can be varied and the phase front of the antennabeam produced by the elements will therefore scan electronically.

The type of electronically scanned antenna shown in FIGURE 1 isconventional in the art. The principles of the linear array shown havealso been extended to planer arrays which can propagate atwo-dimensional wave at any angle and in any direction from the surfaceof the planer array. In both the linear and planer array types ofelectronically scanned antennas the phase differences produced by thephase shifters are generally controlled by a computer or by varying theelectrical path length between the source of radio frequency energy andthe individual radiating elements in some other predetermined manner.While these antennas can be electronically scanned fairly rapidly, aconsiderable amount of complicated equipment is necessary to calculate,control and produce the phase shifts needed to do this. Thus, theantenna is usually extremely bulky and complicated. Also the directionalproperties of the electronically scanned antenna may be somewhatlimited.

FIGURE 2 is a diagram which represents certain of the operatingprinciples of the antenna array of the present invention. For thepurpose of explanation, this array may also be considered to beelectronically scanned like the antenna array of FIGURE 1. However,unlike a conventional electronically scanned antenna, the phasediiferences between different antenna elements are controlled by anincoming wave 20 from another station rather than from a computer orother similar device which controls physical phase shifters.

In FIGURE 2 four radiating elements A, B, C and D out of the wholeantenna are shown arranged in a linear array 19. It should be understoodthat as many elements are provided as is needed. Each element, which isdescribed in detail below, is provided with a substantiallyomnidirectional receiving and transmitting antenna, which may be thesame antenna, and an oscillator. The oscillator at each element isprovided with power from a source. In a preferred embodiment of theinvention the source is turned on and off to effectuate transmission ofinformation. This is described below. The parameters of the variouscomponents forming each oscillator are also seproduced by each element'lected to produce the same natural resonant frequency which issubstantially the same and preferably equal to that of the incoming wave20 from the other station. This other station may be on the ground or atany point in space.

In the array 19 of FIGURE 2 power is supplied to the oscillators of theelements A, B, C and D while a signal from the other station is beingbeamed towards it. The signal is received by the individual antennas ofeach of the elements and the received signal triggers the oscillator atthe respective array element A, B, C or D into oscillation in phase withthe signal as it is received by the respective antenna of that element.It should be clear that each elements oscillator will begin to oscillateat the same frequency but at a slightly different phase as determined bythe angle of incidence of the incoming wave with re spect to the lineararray 19. Stated another way, this means that the phase between adjacentoscillators at elements A, B, C and D will be varied in accordance withthe direction of the incoming wave. The signal produced by eachoscillator during the reception of the incident wave is coupled to aradiator, preferably the same antenna used to receive the incomingenergy, for transmission. Thus, each element radiates a wave of the samefrequency, but of slightly different phase, which is in phase with thewave received by that element.

Since each of the oscillators at the respective elements A, B. C and Dis producing a signal at the same frequency but of'a slightly differentphase, the radiated wave fronts of the signals produced by theseoscillators will combine into a constant phase wave front at some pointin space which is determined by the phase differences between thevarious oscillators. This is the same effect produced by theelectronically scanned antenna of FIG. 1. However, the angle of theconstant phase front Wave with respect to the linear array is nowdetermined only by the direction of the incoming wave rather than byphysical phase shifters. As is described below, the resultingoscillations from each of the elements A, B, C and D in the arraycreates a composite wave front at least a portion of which propagates inthe same direction as the direction of the original incoming wave 20.

To explain in greater detail the creation of the phase front by theelement oscillators which propagates in the same direction as theincoming phase front 20, consider that each of the elements A, B, C andD of FIGURE 2 includes a sinusoidal oscillator and a small, individualreceiving and radiating antenna such as a dipole. The power to each ofthe oscillators is off and there is no signal from ground. The ground orother first station now beams a signal of radio frequency energy towardsthe second station carrying the array. After a suitable time fortransmission between the two stations, the array of FIGURE 2 iscompletely immersed within the signal from the first station, termed theground transmitter in FIGURE 2. For clarity of understanding, theincoming wave front 20 coming from the ground transmitter is broken upso that each complete cycle of oscillation consists of 10 equaldivisions of 36. The first eight, portions through 7, are indicated inFIGURE 2. Each of the oscillator elements A through D, beginsoscillation in phase with the incoming wave at the same time but indifferent phase because the phase of the incoming wave is different atA, B, C and D. Thu-s in this simplified illustration, the wave from D is72 behind the phase of the wave from C and the wave from C is 72 behindthe wave from B.

It is possible, by using Huygens principle, to find the wave frontresulting from the waves radiated by elements A through D. To do this,the wave fronts at the same phase must be added geometrically. Theconcentric circles surrounding each element indicate the waves which areradiating from each and the numbers associated with it indicate thephase with reference to some arbitrary datum. Thus C-6 is the waveradiating from element C having a phase of 6 36 or 216. In order to findthe geometric sum of the radiating waves, they must be added so that theidentical phase fronts are brought together. Thus, if the radiating wavefronts are added at the phase 7 36 or 252, the resulting wave front isthat labeled 25-7 in FIGURE 2 which is obtained by adding A-7, B7, C-7and D7, the contributions from each of the elements at the proper phase.The wave fronts indicated by 25-5 and 253 are the resultant wave frontsat phase 5X36 and 3X36 respectively. Since the resulting wave travels inthe direction of increasing phase, it is easy to see that it willproceed from left to right in FIGURE 2.

In operation the oscillators of the four elements A-D of FIGURE 2 areall supplied with power at the same time and are triggered intooperation by the Wave 26 which is impressed upon each elementsoscillator at the time power is applied. Each oscillator beginsoscillation at a different phase but at the same frequency. Thedifference in phase is attributed to the angle between the incoming wavefront 20 and the line of the array. When the resulting transmitted wavesare added by Huygens principle, the result is a transmitted Wave 25traveling in the direction of the original incoming wave. The transmitted wave front 25 is many times stronger than the incoming wave front20 but travels in the same direction.

By placing a reflecting device, such as a corner reflector adjacent thearray 19, the transmitted wave front 25 can be reflected by and sentback toward the direction of the source from which the incident wavefront 20 came. Thus the array of FIGURE 2, when provided with areflector, can transmit a directional beam of energy in a directionexactly opposite to that of the incident beam which triggers the array.Thus, the array 19 when provided with a reflector can be considered as ascanning type of antenna which transmits a beam of energy back in thesame direction from which the incident beam originated. The scanningangle of the array is only dependent upon the angle of incidence of theincoming wave and, as shown below, the angular scanning range is limitedby the type of reflector used.

A conventional corner reflector 26 for the linear array 19 of FIGURE 2is shown in FIGURE 3 and is formed by two sheets of electromagneticenergy reflective material 27 and 28 placed at right angles to eachother. The array 19 of FIGURE 2 is shown having its elements A, B, C andD located within the aperture of the reflector. Incoming wave 20impinges upon the elements of array 19 which produces the transmittedoutgoing wave 25 in the same direction as the incoming wave in themanner described with respect to FIGURE 2. Several portions 30-33 of theoutgoing wave front 25 are shown striking the reflectors 27 and 28.These portions 30-33 undergo a 180 change of direction at the reflectorwalls and are reflected toward the direction of the incoming wave 20.While only the portions 3033 of the transmitted wave front 25 are shownit should be understood that the same reflection is produced for thecomplete wave front 25 so that all of it is reflected by 180 to producethe final wave front 25R. Therefore, a directional beam 25R is producedby the array 19 and reflector 26, this beam being in the oppositedirection to the incoming wave front 20. This means that the beam 25Rwill end up at the source which produced incoming wave 20. The maximumaperture or effective scanning angle range of the antenna array ofFIGURE 3 is approximately 90 as limited by the mouth of the reflector26. The scanning range can be varied by using other types of reflectorarrangements.

The signal transmitted by the other station to trigger the variousoscillators of the array 19 need not be exceptionally strong but only ofsufficient strength to be greater than the noise normally present in theoscillator circuit at each element. The resultant transmitted wave front25R produced by the oscillators is far stronger than the received signaland completely engulfs it as both signals impinge upon the cornerreflector and propagate back in the direction of the incoming signal.

FIGURE 4 shows the principles of the present invention, as describedwith respect to the linear arrays of FIG- URES 2 and 3, extended to aplaner array 35 of elements which can produce a radiated directionalbeam in two dimensions. Array 35 is arranged in front of a cornerreflector 37 which is formed by three sheets of reflective material 38,39 and 40 placed at right angles with respect to each other. The cornerreflector 37 is capable of reflecting by 180 any wave coming into itsaperture. The reflector 37 has an angular range effective over a solidangle of 90, i.e., it covers one octant of a sphere. The array 35 ofelements is suspended in a plane within the aperture of the reflector 37in a manner so that there is little as possible signal energy absorbedby each element and its supporting structure. One manner of doing thisis shown in FIGURE 4 in which a fishnet type of structure is suspendedbetween the outer corners of the pieces 38, 39 and 40 of the corn-erreflector. This fishnet is preferably formed by a number of strands oflight, stringy material, such as nylon, which run in two directions inthe plane of the array. Since the antenna array of the present inventionis not adversely affected to any great degree by small translations orrotations of the elements 42 there is no need for real rigidity in thefishnet and the supporting wires and strings may be quite thin andlight.

At each intersection or at selected intersections of two strands of thefishnet an element 42 is located. These elements 42 are the same aselements A, B, C and D described in the linear array of FIGURES 2 and 3and are shown by the dots on FIGURE 4. The power for the oscillator ofeach of the elements 42 is provided by wires 44 which run along thestrands of the fishnet. Alternatively, these wires could form thefishnet. It is also possible to make the array 35 rigid by mounting theelements 42 on a piece of radiant energy transparent material. Thiswould be, for example, a printed circuit board on which the componentsof the oscillators and the antennas are printed or otherwise placed byusing other suitable techniques such as microelectronic deposition forthe oscillators and strip lines for the antennas. In all types of arraystructures, whether flexible or rigid, the elements 42 are preferablyencapsulated or provided with some other type of environmentalprotection.

The planer array 35 of FIGURE 4 operates in accordance with the sameprinciples as the linear arrays 19 of FIGURES 2 and 3. Depending uponthe direction of the incident wave front the oscillator for each element42 will be triggered into operation at slightly different places toproduce a transmitted wave front traveling in the same direction as theincident wave front. This transmitted wave front is reflected 180 by thereflector 37 and sent back in a direction opposite that of the incomingwave. Because of the planer array 35 and the corner reflector adirectional beam in two dimensions can be received and retransmitted.

It should be noted that the mounting angle of the array 35 with respectto the reflector 37 is not critical since any wave incident to the arraywill always produce the desired result of having the array produce atransmitted wave traveling in the same direction as the incident wave.For example, even if the incident wave phase front is parallel to theplane of the array, the resultant transmitted wave phase front will bein the same direction before it is reflected by 180.

The effective angle of operation of the fishnet antenna of FIGURE 4 is90 solid degrees, or a single octant in space. This antenna could beused on any type of vehicle in which the vehicle or antenna could bestabilized so that the antenna would be within a 90 range of the sourcetransmitting the incoming wave front 20. If this gross stabilizationrequirement is satisfied then the fishnet antenna will retransmit energyin a direction opposite to that of the incoming energy. This grossstabilization to within only 90 is a much simpler requirement to meetthan the requirements imposed by the finer orientation and stabilizationneeded for a directional antenna of the narrowbeam type and it can beachieved relatively simply.

In order to further increase the angular range of the fishnet type ofantenna, two or more could be mounted back to back thereby increasingthe total angular range of the composite antenna by an octant of asphere for each fishnet antenna that is added. Where eight of theseantennas are combined as shown in FIGURE 5, the edges of the reflectorsare trimmed to resemble a sphere and are effective to receive energyfrom any angle without any sort of orientational stability needed forthe vehicle or the composite antenna.

Eight corner reflector fishnet antenna arrays 45 can also be extended,such as by rods 55 from different points of a vehicle as shown in FIGURE6 to cover a complete sphere of operation for receiving and transmittinga directional beam. In this embodiment the antenna array 45 are mountedon a communication satellite 50. The advantages of the embodimentillustrated in FIGURE 6 are that the surface area of the satellite maybe used for mounting solar batteries 52, test and sensing devices, suchas the radiation and particle detectors 53 and 54, and other instruments(not shown).

It should also be understood that the various embodiments of antennasshown in FIGURES 6 and 7 can be modified by removing one or more of thefishnet antennas 45. This, of course, will reduce the overall angularrange of the composite array. In the embodiment of FIGURE 7, removingone of the antennas 45 will make some sort of orientation arrangementnecessary for the vehicle. However, the large angular range provided bythe remaining antennas 45 still reduce the orientation problem to adegree where it can be handled fairly easily.

It should be understood that the fishnet antenna of FIG- URE 4 hasseveral constructional advantages which makes its use particularlyadaptable for certain applications. For example, the antenna may be sentaloft as a package in which the three pieces 38, 39 and 40 forming thecorner reflector 37 are folded one on top of the other with the fishnetarray 35 folded therebetween. In a preferred embodiment of thisarrangement the three pieces of the reflector have springs interposedtherebetween with the pieces being held together by suitable fasteners.At the proper point in space the fasteners are released so that thesprings snap the reflector pieces to the open condition. The reflectoris also provided with suitable catches for holding the pieces in thisopen condition. This provides a relatively simple and compactarrangement for unfolding the antenna in space.

FIGURE 7 shows a circuit for use as one of the eleents 42 of the array35. Here an antenna 60 is provided which both receives the incoming waveand transmits the wave produced by the oscillator. While the antenna isillustratively shown as a dipole it should be understood that any othersuitable type may be used, for example, a feed horn having a common feedelement and open front and back horns pointing toward and away from thereflector, a monopole, slotted waveguide, slotted line, printed slotline antenna, etc. All of these antennas are well known in the art andthe only requirement imposed upon them is that the antenna radiationpattern be capable of operating over an angular range at least equal tothat of the corner reflector. Design of antennas for satisfying thisrequirement is conventional in the state of the art and no furtherdescription thereof is needed.

The signals received by the antenna 60 are coupled to one winding 62 ofa transformer 61. Winding 62 is inductively coupled to a secondtransformer winding 63 which is connected between the base electrode ofa translstor 65 and a point of reference potential. A third transformerwinding 64 which is shunted by a capacitor 68 is connected to thecollector of the transistor by a capacitor 67. Bias is supplied to thetransistor from a suitable power supply (not shown) by the resistors 69and 70 which are connected respectively to the emitter and collectorelectrodes.

The transistor 65 and its associated components form an oscillatorcircuit which produces a signal of a frequency which is determined bythe parameters of the transformer 61 and the capacitor 68. Thisfrequency is selected to be substantially the same as the frequency ofthe incoming wave used to energize the oscillator. The variouscomponents of the transistor are adjusted, for example, by setting thebias voltages and/or by varying the coupling between the transistorwindings 62, 63 and 64 so that the transistor will not beself-oscillating. However, when an incoming wave is received by antenna60 it is coupled to transformer winding 62 and then to the base winding63 to provide a signal to start the transistor oscillating. Feedback isprovided by the winding 64 and a portion of the signal in this windingis coupled to winding 62 for radiation by antenna 60. Thus, the incomingwave from the ground station triggers oscillator 65 into oscillation andsets an initial phase for the oscillator. This incoming wave is notnecessarily needed for continued operation of the oscillator.

While a transistor oscillator circuit has been shown it should beunderstood that any other suitable type of circuit may be utilized. Forexample, a tunnel diode, or other suitable type of semiconductor devicemay be used. Also, the transistor or tunnel diode may be of the printedor microelectronic variety in order to conserve space. The components ofthe circuit may be protected, for example, by encapsulation or othersuitable means. Also, strip line or printed circuit components may beused for transmission line para-meters at high frequencies. While thecircuit shown in FIGURE 7 contemplates that the oscillator for each ofthe elements 42. is an integ'ral part thereof and is suspended on thefishnet antenna, it should be understood that only the receiving andtransmitting antenna portion 60 of each element need be mounted on thefishnet and that the oscillator can be mounted at some other place, forexample, the vehicle or base station on which the structure is used. Inthis case, the fishnet would have wires connecting each of the elementantennas to an individual oscillator which is located'somewhere on thevehicle.

FIGURE 8 shows a circuit for modulating information onto the energyproduced by the elements 42 of the array. Here a transducer 72 generatesthe information which is to be transmitted. The transducer 72 may be ofany suitable type, such as a thermometer, radiation meas- Iuring device,etc. The output of the transduced is applied to a code converter 73which preferably produces a pulsetype code in response to the transduceroutput. This code is applied to a keyer 74 which also has appliedthereto the power supply voltage from a source 75 for all of theoscillators of the elements 42 in the array. The keyer is any suitabledevice, for example, a silicon controlled rectifier, which is renderedconductive during and in response to selected portions of the code, forexample, positive or negative bits thereof. This permits the voltagefrom the supply 75 to be applied to the oscillators so that they will beenergized by the incoming wave.

In operation, the other station which is trying to communicate with thestation having the array 45 will send out a relatively long continuouswave and will receive back a message in the form of bits as determinedby the code converter 73. In a preferred embodiment of the invention thepower supply is energized only during selected periods by a masterswitch such as a timer. This will conserve the power supply and therebyreduce the requirements for batteries if the array is to be used at astation in which the batteries cannot be replaced or recharged readily.

FIGURE 9 shows an embodiment in which the principles of the presentinvention have been extended to a so called Van Atta type array. Here alinear array of antennas 801 80-6, which are illustratively of the horntype, are arranged in two sets 80-1, 802 and 803 and 80-4, 80-5, and80-6 which are disposed about a geometric center. The horn antennas 80-1and 80-6, 80-2 and 80-5, and 80-3 and 804 are connected by therespective transmission media 82, 83 and 84 which have equal electricallengths. The transmission media 82, 83

. and 84 may be of any suitable type such as coaxial lines, Anoscillator 86, 87 andtWo-wire lines, wave guides, etc. 88 is disposed inthe path of each transmission medium 82, 83 and 84.

Considering an approaching wave front 90, it can be seen that this wavefront strikes elements 80-1, 802 and 803 at different times dependingupon the angle of incidence. The wave incident on these three hornantennas travels down the transmission media 82, 83 and 84 and triggersthe respective oscillators 86, 87 and 88. Each oscillator is energizedin phase with the received incoming wave front 90 and produces a signalof the same frefrequency. Thus, the signal continuing down eachtransmission media towards the respective antennas -6, 80-5 and 80-4bears the same phase relationship to the incoming wave front at antennas80-1, 80-2 and 803.

It can be seen that the electrical wave length or path for each of thesignals striking the respective antennas 80-1, 80-2 and 80-3 and exitingthrough the respective antennas 80-6, 805 and 80-4 is the same since thetransmission media 82, 83 and 84 are of equal length. Consequently, thewave front exiting from the antennas 804, 80-5 and 80-6 travel in theopposite direction as the incident wave front 90. This means that thewaves produced by the oscillators form a new wave front which travelsback along the direction from which the received signal was transmitted.Thus, the array of FIGURE 9 produces a 180 reversal in direction betweenthe re ceived signal and the signals produced by the respectiveoscillators. The incident signals impinging upon antennas 80-4, 805 and80-6 will reach the oscillators connected to these antennas after theyhave been triggered by the waves which first impinge on antennas 804,802 and 80-3. Hence, the oscillator will be triggered by the firs-t wavereceived and the signals incident on antennas 80-4, 80-5 and 806 willnot otherwise affect the operation of the system. The reverse would betrue if the incoming wave struck antennas 80-1, 802 and 80-3 last.

The array shown in FIGURE 9 has been described in linear form forsimplicity. It should be obvious that the principles of this array canalso be extended to a planer .array in the same manner as described withrespect to FIGURE 4. Hence, a wave in two dimensions can be produced forre-transmission back to another base station. While the array of FIGURE9 has also been shown as using horn type antennas it should beunderstood that any'other suitable type can be used, for example, adipole, folded dipole, slot line, etc.

In the array of FIGURE 9 half of the antenna area is used for receivingthe signal from the other station and lator receives energy from both ofthe connected horn antennas and conveys it to one of the oscillators.Thus, considering, for example, circulator 92 connected in transmissionmedium 82, the incoming energy picked up by antenna 80-1 is shiftedcounterclockwise by through the circulator 92 and applied to theoscillator 931. Oscillator 93-1 in transmisison medium 82 is triggeredby this energy and the signal it produces is conveyed the remaininglength of the transmission medium 82 to exit through antenna 806.Similarly, the energy picked up by antenna 80-6 is shifted 90 clockwiseby the circulator 92 and applied to the oscillator 936. Oscillator 93-6is energized and its energy is transmitted via antenna 801 The otherantenna pairs work in the same manner. Thus, in the array of FIGURE 10each antenna 80 serves as both a receiving and a transmitting antenna byvirtue of the circulator 92 which is interposed in each of the connectedtransmission medium. This means that all of the antenna area is utilizedfor both transmission and reception. The principles of the linear arrayof FIG- large angular opening by making the horn apertures small withrespect to the mouth of the horn. In many cases this angular range ofoperation can approach 180. Thus, while the fishnet antenna of FIGURE 4is limited in range to one octant by the corner reflector, a planerarray of horn antennas would not be so limited.

It should be understood that each of the various embodiments of arraysshown can be used at either a fixed or a movable station of any type,the latter including aircraft, ships, satellites, etc. Also, while onetype of oscillator circuit has been shown in FIGURE 7 it should beunderstood that any other type of oscillator circuit may be usedincluding those of the crystal controlled type for increased oscillatorfrequency stability. Further, since the arrays use a plurality ofoscillators, failure of any one or several of the oscillators will notseriously detract or destroy the overall performance of the array. Thisis a distinct advantage over those antenna arrays which use only asingle oscillator whose failure will destroy the operation of the entiresystem.

While preferred embodiments of the invention have been described above,it will be understood that these are illustrative only, and theinvention is limited solely by the appended claims.

What is claimed is:

1. An antenna array for transmitting electromagnetic energy in responseto and toward the same direction as the incident electromagnetic energyfrom a source comprising:

a plurality of radiator elements,

including (a) means for receiving the incident electromagnetic energy ata phase in accordance with its position with respect to the phase frontof the incident electromagnetic energy,

(b) normally quiescent oscillator means coupled to said receiving meansfor producing a signal in response to the received incident energy andat a predetermined phase relationship there with,

(c) and means coupling said oscillator means to said receiving means forradiating the signal produced thereby, the signals produced by saidplurality of radiator elements transmitted as energy with a phase whichtravels in the same direction and has the same phase characteristics asthe phase front of the incident energy,

reflector means comprising a corner reflector adjacent the receivingmeans of said radiator elements for reflecting the phase front of thetransmitted energy by substantially 180, and means for mounting at leastthe receiving means of each said radiator element in a predeterminedspaced relationship to said reflector means.

2. An antenna array as set forth in claim 1 wherein said mounting meanscomprises a plurality of strands of flexible material.

3. An antenna array for transmitting electromagnetic energy in responseto and toward the same direction as the incident electromagnetic energyfrom a source comprising:

a corner reflector of a material for reflecting electromagnetic energy,

a plurality of antenna radiator elements,

means for mounting at least a portion of each of said elements in aplaner array in a predetermined spaced relationship with respect to saidreflector at the aperture thereof,

each of said elements including (a) antenna means for receiving incidentelectromagnetic energy at a phase in accordance with its position in thearray with respect to the phase front of the incident energy,

(b) normally quiescent oscillator means coupled each of said elements 12to said antenna means for producing a signal in response to the receivedincident energy and at a predetermined phase relationship therewith, (c)and means for coupling the signal produced by said oscillator means tosaid antenna means for radiation thereby,

the signals radiated by the antenna means of each of said plurality ofradiator elements forming a transmitted phase front of energy whichtravels in the same direction as the incident phase front and is re.flected by said corner reflector for transmission back toward thedirection from which the incident energy originated.

4. An antenna array as set forth in claim 3 wherein said mounting meansincludes a number of strands of flexible material.

5. An antenna array as set forth in claim 3 wherein each said oscillatorincludes means for producing a signal of substantially the samefrequency as the frequency of the incoming signal.

6. An antenna array of the Van Atta type comprising:

a plurality of pairs of antenna elements in which each element of a pairis spaced about a geometric center point,

an electrical transmission medium of the same electrical lengthconnecting the elements of each said pair, circulator means connected toeach said transmission medium,

a pair of oscillator means electrically connected to different points ofeach said circulator means,

one of said oscillator means receiving energy through the circulatormeans from one of the elements of the pair and being energized therebyto produce a signal which is transmitted by the other element of thepair, the other oscillator means receiving energy from the said otherelement of said pair through said circulator and being energized therebyto produce a signal which is transmitted by the said one element of thepair.

7. An antenna array for transmitting electromagnetic energy in responseto and toward the same direction as the incident electromagnetic energyfrom a source comprising:

a plurality of radiator elements, each of said elements including (a)means for receiving the incident electromagnetic energy at a phase inaccordance with its position with respect to the phase front of theincident energy, (b) normally quiescent oscillator means coupled to saidreceiving means for producing a signal in response to the receivedincident energy and at a predetermined phase relationship therewith, (c)and means coupled to said oscillator means for radiating the signalsproduced thereby, the signals produced by said plurality of radiatorelements being transmitted as energy with a phase front which travels inthe same direction as the phase front of the incident energy, meansconnected to each of said oscillator means for supplying electricaloperating power thereto, means connected to said electrical power supplymeans for controlling the application of said electrical power in adesired manner, to thereby modulate the on-ofl condition of theoscillators,

and reflector means adjacent aid radiator elements for reflecting thetransmitted energy by substantially 180.

8. An antenna array operative over an angle of greater than of a spherefor transmitting electromagnetic energy in response to and toward thesame direction as the incident electromagnetic energy from a sourcecomprising:

a member of radiator arrays, each of said radiator ar- 13 14 raysincluding a plurality of radiator elements, each arrays in position withrespect to each other to proof said radiator elements comprising: videan antenna array having an operative angle of (a) means for receivingthe incident electromaggreater than 90 of a sphere.

netic energy at a phase in accordance With its 9. An antenna array asset forth in claim 8 wherein position with respect to the phase front ofthe said reflector means are corner type reflectors and the incidentenergy, corner reflectors of at least two radiator arrays are lo (b)normally quiescent oscillator means coupled cated adjacent one another.

to said receiving means for producing a signal in response to thereceived incident energy and References Clted at a predetermined phaserelationship therewith, UNITED STATES PATENTS (-c) and means coupled tosaid oscillator means for radiating the signals produced thereby, the2510280 6/1950 G-Oddard "'7 343-4006 3,088,106 4/1963 Kmgsford-Srmth343-68 signals produced by said plurahty of radlator 3,098,971 7/1963Richardson 3436.8 X elements being transmltted as energy With a3,196,438 7/1965 Kornpfner 343-100 phase front WhlCh travels III thesame direction 3 202 997 8/1965 scheu 343 835 X as the phase front ofthe incident energy, I

each of said radiator arrays also having a reflector RODNEY D BENNETTPrlLmary Examiner means operative over an angle of or less, of a spherefor reflecting the transmitted energy by sub- CHESTER JUSTUS,Examinerstantiany 20 J. P. MORRIS, Assistant Examiner. and means formounting at least two of said radiator

1. AN ANTENNA ARRAY FOR TRANSMITTING ELECTROMAGNETIC ENERGY IN RESPONSETO AND TOWARD THE SAME DIRECTION AS THE INCIDENT ELECTROMAGNETIC ENERGYFROM A SOURCE COMPRISING: A PLURALITY OF RADIATOR ELEMENTS, EACH OF SAIDELEMENTS INCLUDING (A) MEANS FOR RECEIVING THE INCIDENT ELECTROMAGNECTICENERGY AT A PHASE IN ACCORDANCE WITH ITS POSITION WITH RESPECT TO THEPHASE FRONT OF THE INCIDENT ELECTROMAGNETIC ENERGY, (B) NORMALLYQUIESCENT OSCILLATOR MEANS COUPLED TO SAID RECEIVING MEANS FOR PRODUCINGA SIGNAL IN RESPONSE TO THE RECEIVED INCIDENT ENERGY AND AT APREDETERMIEND PHASE RELATIONSHIP THEREWITH, (C) AND MEANS COUPLING SAIDOSCILLATOR MEANS TO SAID RECEIVING MEANS FOR RADIATING THE SIGNALPRODUCED THEREBY, THE SIGNALS PRODUCED BY SAID PLURALITY OF RADIATORELEMENTS TRANSMITTED AS ENERGY WITH A PHASE WHICH TRAVELS IN THE SAMEDIRECTION AND HAS THE SAME PHASE CHARACTERISTICS AS THE PHASE FRONT OFTHE INCIDENT ENERGY, REFLECTOR MEANS COMPRISING A CORNER REFLECTORADJACENT THE RECEIVING MEANS OF SAID RADIATOR ELEMENTS FOR REFLECTINGTHE PHASE FRONT OF THE TRANSMITTED ENERGY BY SUBSTANTIALLY 180*, ANDMEANS FOR MOUNTING AT LEAST THE RECEIVING MEANS OF EACH SAID RADIATORELEMENT IN A PREDETERMINED SPACED RELATIONSHIP TO SAID REFLECTOR MEANS.